A calendar is initially a way of naming periods of time, usually days, though also of particular cycles such as the seasons. Cycles in a calendar are often measured by the motion of planets and stars. This allows celebrations and festivals to be calculated. We should become more aware of these timetables.
Psychological / Emotional Perspective:
Because time is a self-imposed constraint, when anything that marks time appears in a dream we are being warned of the potential for limitation.
Everyday Material Aspects:
If a calendar appears in a dream there can be more than one meaning. Our attention may be being drawn to the past, present or future and something significant in our lives, or we may be being warned of the passage of time in an important scheme.